1a.Objectives (from AD-416)
To determine the level of ivermectin in the blood serum of pastured cattle that are provided with free-access to a solid, cooked protein supplement that is medicated with ivermectin.

1b.Approach (from AD-416)
Cattle will be placed in a 17-acre pasture and allowed to freely range the entire pasture. A single tub containing an ivermectin-medicated protein block and/or a single tub containing an ivermectin-medicated mineral block will be placed inside a central penning area supplied with water. The protein block and/or mineral block(s) will be weighed prior to allowing cattle access. Once the cattle are allowed access to the treatment block(s), the blocks will be weighed twice per week to determine (by weight) the quantity of material that is being taken in by the cattle. Once per week the cattle will be placed in a chute and a blood sample will be obtained from the jugular vein of each animal in separate vacuum tubes. Blood samples will then be processed to obtain the serum from the whole-blood, and the serum will be frozen for later analysis. Serum samples will be analyzed by HPLC to determine the concentration of ivermectin in each serum sample. All data collected from the study will then be tabulated to establish the amount of medicated material they are taking in and the subsequent concentration of ivermectin in the blood system.

3.Progress Report

During a 40-week study, cattle (11 animals) were provided free-access to a solid, cooked feed supplement protein/mineral block medicated with ivermectin to determine the efficacy and blood serum level of ivermectin in cattle maintained in a pasture infested with a natural population of cattle fever ticks. Weekly inspection of the treated animals showed that cattle ate enough of the product throughout the 40-week period so that no ticks of any stage were able to survive on any of the animals during the final 36 weeks after treatment was started. Throughout the study, the ivermectin level in the blood serum of treated animals remained well above the level estimated to be necessary to prevent ticks from completing their life cycle. Once the ivermectin-medicated product was removed from the cattle, at the end of the 40-week study, no ivermectin remained in the manure of any animal after 1 week, and no ivermectin was present in the blood serum of any animal after 5 weeks. A few ticks still present in the pasture at the end of the study were probably produced by the untreated white-tailed deer that were in the pasture during the study. Thus, while this treatment technology completely eliminated all ticks on cattle within a 40-week period, the presence of untreated free-ranging white-tailed deer prevented the total eradication of the ticks in the pasture.
The ADODR discussed protocols and exchanged summary data with cooperators through multiple on-site visits, teleconferences, and emails.